Spiders - Teacher Background Information

This unit will help children appreciate the place spiders have in the world and
will lessen the fear of spiders caused by misunderstandings. They will begin
activities such as building a spider habitat, constructing a web and reading
about spiders to develop the theme. There are more than 30,000 different types of
spiders known to scientists! Most of them are very tiny animals that help people
by eating insects. The banana spider, the trap-door spider, the purse-web spider,
the garden spider, and the grass spider are just a few of the interesting animals
we're going to learn about.

Spiders are not insects as many people believe. Students will learn the physical
differences between insects and arachnids in this unit. Students will also study
other distinct characteristics of spiders, such as spiders' contribution to
other organisms in nature. Spiders' need for food will be explained as will the
concepts of "prey" and "natural enemies."

Spiders belong to a class of animals called arachnids. They have four pairs of
segmented legs, and can grow a new leg if they lose one. Most spiders have eight
eyes, and they do not have antennae or wings. A spider's body is divided into two
sections, the abdomen and the cephalothorax. The legs, eyes, and mouthparts are
all in the cephalothorax. Most spiders have poison glands and fangs in their
jaws, which they use to inject poison into insects. The venom paralyzes or kills
their prey.

Spiders usually have six fingerlike silk glands called spinnerets located beneath
their abdomen. The silk comes from inside the spider's body as a liquid, thicker
than water. When a spider wants to make a web, it squeezes the silk out of the
two small holes at the back of its body called spinnerets. The moment it hits the
air, the silk dries into a line that looks like a long strand of hair. Many
spiders use their sticky silk webs to catch food, which consists of tiny animals.
Some spiders use silk as draglines, which are long lines of silk the spider hangs
onto as the wind blows it through the air. The spider can always crawl back up
the silk line if it is blown some place it doesn't want to be! Some spiders spin
silk webs, and others line their burrows with silk. Many spiders lay their eggs
in silken sacs. All young spiders, and some adult males, release long silken
threads to float or ride the wind to new areas. This is called ballooning.

Although spiders can live almost anywhere in the world, some like it where
it is very humid, and some like it where it is very dry. Some spiders live
underground and catch their prey by jumping out at them. Others live in trees and
capture their prey in their webs. Others live in our houses. Have you seen them
hanging from the ceiling? Many times a spider's common name tells something about
the spider. Where do you think the garden spider lives? What about the water
spider? A wolf spider? A banana spider?

The tarantula is probably the most feared of spiders. It is very big and can
stretch itself almost to the size of a one-foot ruler - 10 inches. It is furry,
unlike other spiders. It is a nocturnal animal and comes out at night to find
food. It is large enough to eat many animals that smaller spiders can't catch. It
can eat big beetles, toads and frogs. It can even eat small birds, snakes and
lizards. Most spiders live one or two years, but the tarantula takes eight to 10
years to become an adult, and then lives a few more years. Tarantulas can become
pets in our homes because they can be tamed.

Spiders are considered humankind's friend because they help keep the insect
population in check. Humans use spiders' silk to make threadlike lines for
microscopes, telescopes and other scientific instruments.

All animals have natural enemies. Birds, insects such as wasps, snakes, lizards,
frogs and fish eat spiders. Sometimes spiders eat each other. Humans try to
destroy them because we do not understand how useful they are. Spiders try to
protect and defend themselves from their enemies. Ask students to consider if
they were spiders what they would do to protect and defend themselves. All of us
know how to protect ourselves using methods that are very similar to those of the
spider.

1. Escape! How? (Use the dragline to drop into space and wait; move along
the web to a safe place; use powerful jaws on smaller animals; use venom.)
Usually spiders are frightened of people and try to escape from us because we
appear like giants to them. Humans also try to escape from things that we think
are dangerous.

2. Hide! A spider can hide by using its colors and patterns for camouflage to
blend in with colors and patterns. What colors do spiders have? What are the
colors of dirt, trees, leaves and grass? Humans will also hide if they sense a
danger.

3. Frighten the enemy! Many people think that all spiders are poisonous, but
in general, very few spider bites will be harmful to humans. Tarantulas look
frightening, but they are not poisonous. They just scare their enemies and people
silly!

4. Use a weapon - venom! Most spiders are not poisonous, but some are: the
black widow and the brown recluse are poisonous and make people very ill with
their bites. Many people do not understand that spiders very rarely attack their
enemies. If a spider sees an enemy, it will usually try to get away. But all
spiders use their poison in self defense, when escape is impossible.

At times, spiders will not attack their prey unless it is moving. Many insects
have learned that if they do not move, the spider will not detect their motion
vibrations. Spiders that ensnare their prey in their webs do not use their
poison. The spiders that hunt for their prey, or hide on flowers and capture
insects by grasping them with their fangs when the insects come close by, kill
their victims with poison.